Effects of Soil–Structure Interaction on Seismic Fragility of Railway Concrete Bridge, in India

Abstract

This paper is a comparative case study about seismic fragility surfaces of a railway-bridge pier considering with and without soil–structure interaction effect. The probability of exceedance of damage by the piers is the primary concern of this study's fragility analysis. Lateral stiffness and horizontal stiffness are calculated layer-wise based on the soil profile. The study also focused on single parameters such as pier tip, base absolute maximum displacement, and spectral acceleration. Considering the bridge selected, a modal analysis was performed through nonlinear time-history analysis with a set of scaled real recorded ground motions data applicable for the study location to capture the actual characteristics of motion that may be experienced by the structure. Empirical relationships were established between pier tip, base displacement, and rotation with spectral acceleration by the multiple linear regression method. The first case showed the effect of soil overpowers the fragility curves. Fragility surfaces were generated for the second case, considering both without and with soil–structure interaction effect. The result shows that the soil–structure interaction effect reduces the probability of damage and the effect depends on soil type. However, the variation is marginal in soft soil. The pier tip and base rotation become a decisive guiding factor for without soil effect; however, rotation effects become more while considering soil effect, but the pier tip and base displacement show opposite results. However, the soil provides more stiffness and stability to the structure to resist seismic forces. The study could be enhanced if the soil properties are altered and the analysis performed for higher magnitude seismic excitations.